There is a continuing effort to develop novel methods for reducing agricultural losses. Significant loss may be attributed to vertebrates, for example, rodents. Although limited data are available that document the distribution and magnitude of agricultural losses caused by vertebrates (Salmon, T. P., "Evaluating rodenticide use impacts on agricultural production," in Vertebrate Pest Control and Management Materials, 5th Vol., pages 115-127, Shumake and Bullard eds., American Society for Testing and Materials, Philadelphia, Pa. (1988)), such losses are believed to be substantial (Marsh, "Rodent problems on the North American continent," in Rodent Pest Management, pages 1-12, I. Prakash ed., CRC Press Inc., Boca Raton, Fla. (1988)), and damage is likely to increase in the future as conservation tillage practices become more widespread.
It is generally recognized that rodents, for example, rats (e.g., Rattus norvegicus, Rattus rattus), mice (e.g., Mus musculus, Peromyscus maniculatus), voles (e.g., Pitymys pinetorum, Microtus pennsylvanicus), and various ground squirrels (e.g., Citellus spp.), cause greater economic harm than other vertebrates. Brooks et al., A Training Manual on Vertebrate Pest Management, page 206, Pakistan Agricultural Research Council, Islamabad, Pakistan (1990); Castrale, "Impacts of conservation tillage practices on farmland wildlife in southeastern Indiana," Indiana Statewide Wildlife Research Report No. W-26-R-18, page 28 (1987). Significant losses to feed, forage, oil and fiber crops are attributed to rodent consumption before harvest, and harvested materials are further depleted by rodents during transportation and storage.
Rodents are also indirectly responsible for livestock loss to disease. Rodents serve as primary reservoirs or hosts to vectors for human and livestock diseases, including viral zoonoses (e.g., Venezuelan equine encephalitis), rickettsial diseases (e.g., Rocky mountain spotted fever) and bacterial diseases (e.g., salmonella). Gratz, "Rodents and human disease: a global appreciation," in Rodent Pest Management, Pages 101-170, I. Prakash, ed., CRC Press Inc., Boca Raton, Fla. (1988). Livestock loss to such diseases may be economically significant, and the potential for transmission to humans presents serious health concerns.
In addition to causing agricultural losses, commensal rodents are responsible for structural damage. Rodents undermine and weaken structures (Marsh, "Rodent problems on the North American continent," in Rodent Pest Management, page 1-12, I. Prakash ed., CRC Press Inc., Boca Raton, Fla. (1988); Timm, "An IPM approach to rodent control on midwestern farms," in Proceedings of the Tenth Vertebrate Conference, Pages 147-150, R. E. Marsh ed., Univ. of California, Davis (1982)), and chew through electrical and telephone cables. Rodents are particularly attracted to containers for discarded refuse, packaging, fabrics, and plastics.
Rodent predation of trees actually hinders reforestation efforts. Mountain beavers (Aplodontia rufa), hinder reforestation on more than 121,500 ha of otherwise highly productive land in the Pacific Northwest. Campbell and Evans, "Recent approaches to controlling mountain beavers (Aplodontia rufa) in Pacific Northwest forests," Proc. Vertebr. Pest Conf. 13:183-87, Davis, Calif. (1988). The most common form of damage is the cutting of seedlings. Clipped seedlings often die and those trees which do survive generally suffer retarded growth and deformities. Borrecco and Anderson, "Mountain beaver problems in the forests of California, Oregon and Washington," Proc. Vertebr. Pest Conf., pages 135-42, Fresno, Calif. (1980). Further, mountain beavers will girdle adult trees and crop branches. The longevity of trees and the continuing need for protection makes them a difficult crop to safeguard from predation.
Various methods, for example, trapping (Evans, "Mountain beaver damage and management," Proc Symp. Animal Damage Management in Pacific Northwest Forests, pages 73-74, Spokane, Wash. (1987)), poisoning and mechanical barriers (Campbell and Evans, supra) have been used in an attempt to control rodent predation of trees. Likewise, habitat manipulation and the destruction of burrow systems has the potential to displace animals and thereby reduce predation. However, each of these methods is costly, and with the exception of poisoning, each is difficult to implement on a large scale.
Chemical repellents are generally preferred to mechanical barriers, in part, because chemical aversive agents may be employed on a large scale, relatively economically. Chemical agents, such as Big Game Repellent (BGR-P; fermented egg products), may be applied directly to the locus from which rodents are to be repelled. Mountain beaver damage to trees to which BGR-P was provided is significantly less than that inflicted on untreated trees. Campbell, et al., "Evaluation of BGR-P repellent to protect Douglas-fir seedlings from damage by mountain beavers," USDA APHIS Denver Wildlife Research Center, Special Report, Olympia, Wash. (1987). However, with the exception of Big Game Repellent (BGR-P), no such aversive chemicals have been available for use against rodents. Campbell, et al., supra.
Damage may be further reduced by providing the area around the trees with chemical repellents that make the area uninhabitable. For example, pocket gopher (Thomomys talpoides) avoid burrows that have been treated with predator odors. Sullivan, et al., "Use of predator odors as repellents to reduce feeding damage by herbivores III. Montane and meadow voles (Microtus montanus and Microtus pennsylvanicus)," J. Chem. Ecol. 14:363-78 (1988).
As a cost effective measure, chemical repellent treatments may be limited to seasons when damage is most likely to occur. For example, at high elevations Douglas fir are predominately taken during winter and spring when other forage is not readily available and the nutritional value of conifers is high. O'Brian, "Seasonal selection of coniferous trees by the sewellel Aplodontia tufa," Mammalia 52:325-30 (1988).
Chemical repellent agents may also be employed to decrease agricultural losses directly traceable to rodent consumption and to reduce the indirect losses attributed to rodent infestation, such as livestock loss to disease. Rodent utilization of functional articles, such as electrical and telephone cables, refuse containers, and the like, may be reduced by chemical rodent repellents. Such repellents may be applied directly to the locus from which rodents are to be repelled or to the area around the locus. Such repellents may also be incorporated in polymers for use in making the functional articles. Similarly, rodent utilization of other materials, in particular, trees, may be reduced by chemical rodent repellents. Such repellents may be applied directly to the trees, or to the area around the trees, for example, the rodent burrows. Chemical repellents may be used to prevent rodent infestation or preempt reinvasion. Selective application of chemical rodent repellent agents, for example, application during seasons when damage is most likely to occur, may be a cost effective method of reducing rodent utilization of materials susceptible to such utilization.
Feedlot depredation and livestock loss to disease may be reduced by decreasing rodent attraction to livestock feedlot and/or water supply, which may be measured as a reduction in rodent consumption of such provisions. There are a number of identified avian aversive agents that may be safely added to livestock feed without affecting the palatability of such feed. However, repellency in birds is substantially different than that in mammals. Szolscanyi, J., et al. "Nociception in pigeons is not impaired by capsaicin", Pain 27:247-260 (1986); Mason, J R , et al ,. "Exploitable characteristics of neophobia and food aversions for improvements in rodent and bird control", Pages 20-39 in D E. Kaukienen, ed. Vertebrate pest control and management materials. Am. Soc. for Testing and Materials, Philadelphia, Pa. 315pp (1983). Thus, although methyl anthranilate (MA), a known bird repellent agent is palatable to humans and livestock (Furia and Bellanca, Handbook of flavor ingredients, at page 346, CRC Press, Cleveland, Ohio (1975); Glahn, et al,. "Dimethyl anthranilate as a bird repellent in livestock feed," Wildl Soc. Bull. 17:31-320. 1989), research indicates that it is accepted by rodents such as deer mice. Schafer and Bowles, "Acute oral toxicity and repellency of 933 chemicals to house and deer mice." Arch., Environ. Contam. Toxicol. 14:111-129 (1985). Repellents like capsaicin or denatonium saccharide and denatonium benzoate are either broadly offensive to all mammals (Meehan, "Chemical repellents," in Rodent Pest Management, pages 399-406, I. Prakash ed., CRC Press Inc., Boca Raton, Fla. (1988)), or show considerable inter- and intra-specific variability in effectiveness, thus making their performance unpredictable.
At present, there are several substances that can act as rodent repellents, for example, capsaicin. However, these substances are generally either toxic or aversive to humans and domestic livestock. A promising strategy for the development of new rodent repellents may be molecular modelling where chemical structure is related to biological activity. This approach was used to test 36 derivatives of benzoic acids as bird repellents. Mason, et al., "Ortho-aminoacetophenone repellency to birds: similarities to methyl anthranilate," J. Wildl. Management 55:334-40 (1991); Clark and Shah, Nonlethal bird repellents: in search of a general model relating repellency and chemical structure," J Wildl. Management 55:538-45 (1991); Clark, et al., "Chemical repellency in birds; relationship between chemical structure and avoidance response," J. Exp Zoology 260:310-22 (1991). Three molecular features contribute to avian repellency: (1) the basicity of a substituted phenyl ring; (2) the presence of an electron-donating group in resonance with an electron withdrawing group on a phenyl ring; and (3) a heterocyclic ring in the same pi cloud plane as the phenyl ring, the ring comprised of an intramolecular hydrogen bond or covalently bonded heteroatoms. Clark and Shah, supra.
With reference to the foregoing, it is clear that there is a need for methods to reduce rodent consumption or utilization of materials susceptible to rodent consumption or utilization. In these methods, chemical aversive agents are generally preferred to mechanical means, and non-lethal chemical repellent agents are further preferred. In addition to the aforementioned utility, such non-toxic repellent agents may be used to reduce the health hazard granular agricultural chemicals present to rodents and birds that unwittingly ingest them. A non-toxic chemical agent which repels both rodents and birds and which may be included in the manufacture of hazardous agricultural chemicals would have considerable utility. At present, no such repellent exists. Beauchamp and Mason, "Comparative hedonics of taste," in The Hedonics of Taste, pages 159-183, Bolles ed., Lawrence Erlbaum Assoc., Hillsdale, N.J. (1991).
There is a need for non-toxic rodent repellent agents that may be added to livestock feed and/or water supply without affecting the palatability of such provisions. There is a further need for rodent repellent agents which may be used directly or indirectly to protect trees from predation and/or which may be applied to or incorporated into polymers used to make functional articles which are susceptible to being utilized or damaged by rodents. There is still a further need for non-toxic rodent repellent agents that may be applied to crops to decrease rodent consumption both before and after harvest. Heretofore, such non-toxic rodent repellents have not been available.